Patent GB-702200-A (GB)
Title: Improvements in mixed grain colour photography
IPC: G03C7/30
Filed: 1949-10-29
Abstract: 702,200. Mixed grain colour photography. KODAK, Ltd. Oct. 29, 1949 [Oct. 30, 1948], No. 27762/49. Class 98(2) A reversal process for producing a multicoloured record of a multicoloured object or image comprises exposing a layer containing at least two sets of differentially sensitized silver halide grains, a first of which sets has, in the concentration employed, a sensitizing dye which sensitizes at a desired sensitizing maximum but in a lower concentration sensitizes at a different sensitizing maximum, usually at a shorter wave length, whereby diffusion of the dye on to any other set of grains sensitizes them at such different sensitizing maximum; to coloured light from a multicolour object or image or from colour separation records thereof; developing all the sets of grains in a black and white developer, re-exposing the layer uniformly with light in a wave band which includes the sensitizing maximum of said first set of grains but excludes both the sensitizing maximum of any other set of grains and the principal region of sensitization by dye diffused from the first set of grains, colour developing the grains thereby exposed, re-exposing the layer uniformly with light in a wave band which includes the sensitizing maximums of a second set of grains, colour developing the grains thereby exposed and subsequently removing developed silver from the layer to leave positive dye images therein. Preferably the first set of grains is provided with a red sensitizing dye and the second set with a green sensitizing dye and both of the dyes have the specified diffusion property. Such layer may include a third, blue sensitive, set of grains, and in this case the re-exposing lights are such as to exclude the sensitizing maxima of this third set of grains and of that caused by dyes diffused from the first and second sets of grains. Example 1 is directed to the production of cyan and magenta part images suitable for a 3-colour process, and describes with full quantitative details the use of 3:31-dimethyl-9- ethyl-4:5:4<SP>1</SP>:5<SP>1</SP>-dibenzthiacarbocyanine chloride as red sensitizer and 1<SP>1</SP>:3-diethyl-5-phenyl-6<SP>1</SP>- methoxythia-2-cyanine bromide as green sensitizer in silver bromoiodide emulsions and Wratten Nos. 70 and 16 filters respectively for reversal reexposure. The word Wratten is a Registered Trade Mark. 3-colour procedure by overcoating a layer as of example 1 with a high contrast emulsion containing a removable yellow filter dye; and also by inclusion in such layer of highly blue sensitive bromoiodide or blue sensitized chlorobromide grains and with use of a combination of Wratten 16 and 63 filters for the green re-exposure to avoid eventual magenta development at the expense of yellow dye of the blue sensitive grains to which red sensitizer has diffused is described. Example 2 describes the use of 3: 31-dimethyl-8: 10-toloxythiacarbocyanine bromide as red sensitizer and 1<SP>1</SP>: 3- diethyl-4: 5-benz-6<SP>1</SP>-methylthia-2<SP>1</SP>-cyanine bromide as green sensitizer; and example 3, similarly, 3: 3<SP>1</SP>- dimethyl-9-phenyl-4 : 5 : 4<SP>1</SP> : 5<SP>1</SP>-dibenzthiacarbocyanine chloride and 3:3<SP>1</SP>:9-triethyl-5:5<SP>1</SP>diphenyloxacarbocyanine bromide, both for processing as in example 1 to cyan and magenta fast images. In example 4 a mixed grain emulsion as of example 3 includes also chlorobromide grains blue sensitized with 3: 31-diethyl-6: 7: 6<SP>1</SP>: 7<SP>1</SP>-dibenzthiacyanine chloride and processing for this including a final re-exposure to white light and yellow colour development other suitable sensitizing dyes for red and green are described with reference to Specifications 378,870, [Group IV], 378,885; 380,140, 408,277, [both in Group IV], 496,116 and 592,267. Specification 702,255 also is referred to. The Specification as open to inspection under Sect. 91, comprises also negative positive processes using these mixed grain emulsions. This subjectmatter does not appear in the Specification as accepted.